Re: [boost] [atomic] Probable documentation issue: how do weknowatomic is safe and/or efficient?

On Wed, Dec 25, 2013 at 4:47 PM, Andrey Semashev wrote:

On Wed, Dec 25, 2013 at 4:40 PM, Rob Stewart wrote:

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On Dec 24, 2013, at 2:24 PM, Andrey Semashev wrote:

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On Tuesday 24 December 2013 17:17:37 John Maddock wrote:

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I'm sure the answer to (a) is that it is correct, but I was surprised that atomic<int> relied on the volatile modifier for thread safe load/stores on MSVC, I had assumed that something more than that would have been required, but I know I'm out of date on this stuff!

"volatile" was changed in VC++ 8.0 to guarantee acquire/release semantics, then changed back in 2012 to only do so when /volatile:ms is active, which it is by default, except on ARM.

http://msdn.microsoft.com/en-us/library/12a04hfd.aspx

So does this mean that Boost.Atomic is perhaps not safe after all?

No, it's perfectly safe on x86. It is also safe on ARM if /volatile:ms is specified.

How do you ensure the use of /volatile:ms? Can users build Boost with /volatile:iso?

You can't, I was just answering John's question.

To be clear, yes, I agree that this needs fixing. It's just no one got around to do it. A ticket would be welcome. Especially, with a patch. :)

I have updated Boost.Atomic (develop branch) so that it should work on Windows ARM, but I don't have hardware to test it. To my knowledge, none of our testers have the hardware as well. So I would appreciate if someone tried it out and reported the results (both positive and negative). Thanks.